Twisted pair wires are simple and inexpensive and therefore perhaps the most commonly used type of cable for low voltage signal transmission. The most common use of twisted pair wires is in telephone circuits. Unused twisted pair telephone cable currently installed in buildings is however often adequate for applications other than telephone circuits, such as for local area networks. For example, IEEE 802.3 10 Base T (Twisted Pair Ethernet) local area networks and 4 and 16 Mbps token ring local area networks can use unshielded twisted pair cable. For new installations, unshielded twisted pair cable is less expensive than coaxial cable or shielded twisted pair cable. Technicians also have significant twisted pair installation experience.
Use of twisted pair cable for many network applications requires signal conditioning or noise suppression. Common mode chokes, isolation transformers and filters, or some combination of one or more of these three, are often necessary. Chokes provide common mode rejection and impedance matching. The transformers provide dc isolation. LC filters can be used to filter out high frequency noise. Typically, these signal or line conditioning components and simple circuits are located on the network node or hub board to which the twisted pair cable is attached. Some form of standard modular jack or modular telephone jack is used to connect the cable to the node or hub printed circuit board. One specified interconnection for 10 Base T networks, or the medium dependent interface connector, is an eight position modular jack, which is referred to as a RJ-45 jack. These signal conditioning or noise suppression components are conventionally located on the printed circuit board between the connector and the processor used in the hub, medium attachment unit, transceiver circuit, multiport repeater, node or other network unit. Transmit and receive lines can each require signal conditioning. A large number of processors are available for such applications. For example, the Intel 82504 can be used in the analog front end of a 10 Base T node. These signal conditioning components can be discretely mounted on printed circuit boards or they can be manufactured as a separate subassembly which can then be mounted on a printed circuit board. These separate subassemblies can include chokes, chokes plus transformers, or they can be choke, transformer, filter subassemblies.
Although existing local area networks can require this type of signal conditioning or noise suppression, some form of signal conditioning is often necessary for other applications. For example, telephone circuits can require common mode chokes. For higher performance systems currently under consideration, such as 100 mbps local area networks, even more sophisticated signal conditioning or noise suppression will be necessary.
There have been a number of prior art electrical connectors which have incorporated the connector and a filtering circuit into one subassembly. U.S. Pat. No. 4,726,638 is one example of a modular telephone jack with discrete diodes between each lead and ground. These diodes are mounted on a small printed circuit board. A slot on the back of the modular telephone jack housing receives the printed circuit board, which is positioned parallel to the bottom of the telephone jack. Each telephone jack lead is soldered to the printed circuit board at the rear. The diodes are mounted between each lead and ground and not between the ends of the lead, so it is not necessary to separate the lead when it is soldered to the printed circuit board.
A subassembly of an electrical connector and a signal conditioning circuit offers several advantages. Printed circuit board real estate on the main hub or node board is conserved because additional circuitry is now located within the connector foot print or in a space less than the sum of the space otherwise occupied by the connector and separate signal conditioning circuitry. Final assembly of the main printed circuit board requires fewer components. The printed circuit board conductors are also shorter and should therefore be less susceptible to external noise.
The connector subassembly of U.S. Pat. No. 4,726,638 includes, however, a relatively simple noise suppression circuit. For applications such as local area networks, multiple components are needed on multiple lines. The size of the substrate on which these multiple components are mounted must remain relatively small, if all of the advantages of this subassembly are retained. Mutual interference between signal conditioning components may also be a problem and the placement of the various electronic components can be quite critical. Placement is a problem, even for prior art devices in which the signal conditioning components are placed on the printed circuit board. In order to maintain proper component placement in such assemblies, it is common practice to mechanically fix components in place. These components can be mechanically fixed in place by potting the components with an epoxy, or other bonding agent, or by insert molding a number of components in a physical subassembly.
Insert molding is used in other applications to retain electrical elements in position. For example, U.S. Pat. No. 5,362,257 discloses an eight conductor modular jack assembly in which crossing leads are maintained in position by insert molding plastic around the leads. Insert molding is also used to encapsulate many standard integrated circuit components. The modular jack disclosed in U.S. Pat. No. 5,362,257 also comprises an easily assembled two component assembly in which an insert molded lead subassembly is mated with a separate housing assembly.
Other modular jack subassemblies incorporating chokes in a telephone jack housing are shown in U.S. Pat. No. 5,015,204 and U.S. Pat. No. 5,069,641. U.S. Pat. No. 5,015,204 discloses a modular jack assembly in which jack leads are wound around a choke coil. U.S. Pat. No. 5,069,641 discloses a modification of this other patent in which the choke coil and lead segments are soldered to a printed circuit board. This printed circuit board assembly is then encased in an insulating housing consisting of a base and a lid and having two internal chambers. The choke coil printed circuit board is mounted in one chamber which is separated by a separator from a chamber adapted to receive a modular plug. This latter device is assembled by inserting the choke coil printed circuit board subassembly in the housing and inserting the terminal leads through the bottom of the housing base. The contactor on the opposite end extends over the separator into the plug receiving chamber. A lid is then attached to encase the choke coil printed circuit board subassembly. Although this patent depicts only the use of a choke coil, it does suggest that chip inductors and chip capacitors, etc. could also be used. Although not addressed in U.S. Pat. No. 5,069,641, adaptation of that approach to 10 Base T and Token Ring applications would in all likelihood require encapsulation of the components by insert molding or potting them prior to assembly in the housing, or by potting the printed circuit board subassembly after insertion in the housing chamber.
None of these prior art devices depict a modular jack assembly suitable for use in a broad range of network applications and suitable for use at frequencies such as those encountered in 10 Base T, token ring, or networks having even higher data rates, such as proposed 100 Mhtz. networks. None of these devices show a network jack assembly in which chokes, chokes and transformers, or choke, transformer, filter combinations can be positioned in series with multiple leads in a modular jack. None of these devices depict a network jack assembly in which each of these multiple components can be precisely positioned and in which that precise positioning can be maintained over the life of the device to insure that consistent electrical performance can be achieved among multiple devices and over the life of a single device. None of these devices show a modular jack assembly in which the electronic components can be protected. None of these devices disclose a modular jack assembly which can be fabricated by positioning the components on a small printed circuit board, insert molding leads to be connected to this printed circuit board and then mating this subassembly with a modular jack housing having a profile for receiving a modular plug. An assembly having all of these features would be more easily assembled than, for example the assembly of U.S. Pat. No. 5,069,641. The insert molded subassembly would stabilize the position of the leads, which would not have to be inserted in holes in the bottom of the housing to provide sufficiently precise positioning for lead placement in printed circuit board plated through holes or on surface mount pads.
A signal transmission jack which addresses each of these shortcomings is disclosed in a co-pending application entitled Electrical Connector Jack for Signal Transmission, Serial No. 08/384,086, was filed in the name of Venkat Raman on the same date as the parent application and is hereby incorporated by reference. That modular jack has the same lead footprint as a standard RJ-45 jack and used one of the eight leads in the standard footprint as a connection to ground. In that co-pending application, the printed circuit board subassembly and the leads are encapsulated, preferably by insert molding.
In some cases, it is desireable to replace the electronic components on the printed circuit board subassembly either for purposes of repair, modification, or upgrade in the circuitry connected to the modular jack. There is a need, therefore, for an upgradeable modular jack assembly.